In a communications system, such as a cellular wireless system, it is known that the SIR of a received signal is a useful signal quality parameter for various procedures. In the case of a system using two or more antennas providing diversity path signals which are subject to fading, the SIR of each path is a particularly useful parameter for use in selection or combining of the diversity path signals for optimum communications. The SIR may also be used in connection with processes such as hand-off, adaptive channel allocation, dynamic power control, and cell tiering.
It is desirable, especially for use for diversity path signal selection or combining, to provide a rapid and accurate determination of SIR for each diversity path signal. The requirements for speed and accuracy conflict with one another, in that typically averaging processes have been used to enhance the accuracy of SIR determination, which slows the determination process. Ideally, a very accurate determination of SIR would be provided instantaneously for each sample of the received signal.
It is also desirable to determine SIR in a receiver having only a single antenna, to determine SIR without reliance on any training sequence or pilot signal, and to achieve this in a manner that is reliable, simple, and easy to implement.
In the case of communications with mobile communications devices or terminals, it can also be important to determine the relative speed at which a terminal is moving. This speed determines the Doppler bandwidth of signals received from the terminal, and affects communications parameters such as fading, and hence SIR, and time requirements for hand-off. Consequently, a determination of the Doppler bandwidth of a received signal also provides useful information.
Objects of this invention are to provide improved methods of and apparatus for determining SIR and Doppler bandwidth of a received signal in a communications system.